Prevalence and characterization of renal tubular acidosis in patients with osteopenia and osteoporosis and in non-porotic controls

NBCe1-B/C-knockout mice exhibit an impaired respiratory response and an enhanced renal response to metabolic acidosis

The sodium-bicarbonate cotransporter (NBCe1) has three primary variants: NBCe1-A, -B and -C. NBCe1-A is expressed in renal proximal tubules in the cortical labyrinth, where it is essential for reclaiming filtered bicarbonate, such that NBCe1-A knockout mice are congenitally acidemic. NBCe1-B and -C variants are expressed in chemosensitive regions of the brainstem, while NBCe1-B is also expressed in renal proximal tubules located in the outer medulla. Although mice lacking NBCe1-B/C (KOb/c) exhibit a normal plasma pH at baseline, the distribution of NBCe1-B/C indicates that these variants could play a role in both the rapid respiratory and slower renal responses to metabolic acidosis (MAc). Therefore, in this study we used an integrative physiologic approach to investigate the response of KOb/c mice to MAc. By means of unanesthetized whole-body plethysmography and blood-gas analysis, we demonstrate that the respiratory response to MAc (increase in minute volume, decrease in pCO2) is impaired in KOb/c mice leading to a greater severity of acidemia after 1 day of MAc. Despite this respiratory impairment, the recovery of plasma pH after 3-days of MAc remained intact in KOb/c mice. Using data gathered from mice housed in metabolic cages we demonstrate a greater elevation of renal ammonium excretion and greater downregulation of the ammonia recycling enzyme glutamine synthetase in KOb/c mice on day 2 of MAc, consistent with greater renal acid-excretion. We conclude that KOb/c mice are ultimately able to defend plasma pH during MAc, but that the integrated response is disturbed such that the burden of work shifts from the respiratory system to the kidneys, delaying the recovery of pH.

The pathophysiology of distal renal tubular acidosis

The kidneys have a central role in the control of acid-base homeostasis owing to bicarbonate reabsorption and production of ammonia and ammonium in the proximal tubule and active acid secretion along the collecting duct. Impaired acid excretion by the collecting duct system causes distal renal tubular acidosis (dRTA), which is characterized by the failure to acidify urine below pH 5.5. This defect originates from reduced function of acid-secretory type A intercalated cells. Inherited forms of dRTA are caused by variants in SLC4A1, ATP6V1B1, ATP6V0A4, FOXI1, WDR72 and probably in other genes that are yet to be discovered. Inheritance of dRTA follows autosomal-dominant and -recessive patterns. Acquired forms of dRTA are caused by various types of autoimmune diseases or adverse effects of some drugs. Incomplete dRTA is frequently found in patients with and without kidney stone disease. These patients fail to appropriately acidify their urine when challenged, suggesting that incomplete dRTA may represent an intermediate state in the spectrum of the ability to excrete acids. Unrecognized or insufficiently treated dRTA can cause rickets and failure to thrive in children, osteomalacia in adults, nephrolithiasis and nephrocalcinosis. Electrolyte disorders are also often present and poorly controlled dRTA can increase the risk of developing chronic kidney disease.

Long-term complications of primary distal renal tubular acidosis

The clinical manifestations of primary distal renal tubular acidosis usually begin in childhood, but the disease is caused by a genetic defect that persists throughout life. This review focuses on the complications of distal tubular acidosis that occur or remain long-term such as nephrocalcinosis and urolithiasis, growth impairment, bone mineralization, severe hypokalemia, kidney cysts, and progressive kidney failure, as well as other persistent manifestations that occur independent of acidosis but are associated with some inherited forms of the disease. The pathogenic factors responsible for kidney failure are discussed in particular because it is a complication to which different publications have recently drawn attention and which affects a high percentage of adults with primary distal renal tubular acidosis. The need to maintain optimal metabolic control of the disease and scheduled clinical follow-up throughout life and the importance of organizing protocols for the transition of patients to adult nephrology services are emphasized.

Preclinical and Clinical Evidence of Effect of Acid on Bone Health

Acid can have ill effect on bone health in the absence of frank clinical acidosis but affecting the bone mioneral matrix and bone cells via complex pathways botyh ascute;y and chronically. While the reaction of bone to an acid load is conserved in evolution and is adaptive, the capacity can be overwhelmed resulting in dire consequences. The preclinical an clincl evidence of the acdi effect on bone is very convincing and the clinical evidence in both association and interventiopn studies are also quite credible, The adverse effects of acid on bone is underappreoicated, under-investigated, and the potential benefits of alkali therapy is not generrally known.

Evaluation of urinary acidification in children: Clinical utility

The kidney plays a fundamental role in acid-base homeostasis by reabsorbing the filtered bicarbonate and by generating new bicarbonate, to replace that consumed in the buffering of non-volatile acids, a process that leads to the acidification of urine and the excretion of ammonium (NH₄ ⁺). Therefore, urine pH (UpH) and urinary NH₄ ⁺ (UNH₄ ⁺) are valuable parameters to assess urinary acidification. The adaptation of automated plasma NH₄ ⁺ quantification methods to measure UNH₄ ⁺ has proven to be an accurate and feasible technique, with diverse potential indications in clinical practice. Recently, reference values for spot urine NH₄ ⁺/creatinine ratio in children have been published. UpH and UNH₄ ⁺, aside from their classical application in the study of metabolic acidosis, have shown to be useful in the identification of incomplete distal renal tubular acidosis (dRTA), an acidification disorder, without overt metabolic acidosis, extensively described in adults, and barely known in children, in whom it has been found to be associated to hypocitraturia, congenital kidney abnormalities and growth impairment. In addition, a low UNH₄ ⁺ in chronic kidney disease (CKD) is a risk factor for glomerular filtration decay and mortality in adults, even in the absence of overt metabolic acidosis. We here emphasize on the need of measuring UpH and UNH₄ ⁺ in pediatric population, establishing reference values, as well as exploring their application in metabolic acidosis, CKD and disorders associated with incomplete dRTA, including growth retardation of unknown cause.

Vitamin D Deficiency, Osteoporosis and Effect on Autoimmune Diseases and Hematopoiesis: A Review

Vitamin D (VD) is essential for bone homeostasis, but it is also involved in pleiotropic effects on various organs and tissues. In adults, VD deficiency can cause or exacerbate osteoporosis and induce osteomalacia. However, every tissue and cell in the body has a VD receptor, including the brain, heart, stomach, pancreas, skin, gonads, and immune cells, and a deficiency may modify the function of these organs. Thus, the wide-ranging actions of VD help to explain why a reduction in VD amount has been correlated with numerous chronic diseases. In fact, VD deficiency increases the risk of osteoporosis and several other diseases and complications characterized by impaired bone metabolisms, such as autoimmune diseases, inflammatory bowel diseases, allergy, endocrinological diseases, hematological malignancies, and bone marrow transplantation. This review aims to investigate the link between VD deficiency, osteoporosis, and its concomitant diseases. Further epidemiological and mechanistic studies are necessary in order to ascertain the real role of hypovitaminosis in causing the reported diseases; however, adequate vitamin supplementation and restoration of metabolic normality could be useful for better management of these pathologies.

Distal Renal Tubular Acidosis: ERKNet/ESPN Clinical Practice Points

Distal renal tubular acidosis (dRTA) is characterised by an impaired ability of the distal tubule to excrete acid, leading to metabolic acidosis. Associated complications include bone disease, growth failure, urolithiasis and hypokalaemia. Due to its rarity, there is a limited evidence to guide diagnosis and management, however, available data strongly suggest that metabolic control of the acidosis by alkali supplementation can halt or revert almost all complications. Despite this, cohort studies show that adequate metabolic control is present in only about half of patients, highlighting problems with treatment provision or adherence. With these clinical practice points the authors, part of the working groups tubulopathies in the European Rare Kidney Disease Reference network (ERKnet) and inherited kidney diseases of the European Society for Paediatric Nephrology (ESPN) aim to provide guidance for the management of patients with dRTA to facilitate adequate treatment and establish an initial best practice standard against which treatment of patients can be audited.

Evaluating distal renal tubular acidification function in primary hyperparathyroidism and its effects on bone mineral density

Background

Primary hyperparathyroidism (PHPT) is a common endocrinopathy that may increase fracture risk and decrease bone mineral density (BMD). Some patients develop distal renal tubular acidification dysfunction under conditions of hyperchloraemia or hyperchloraemic acidosis. To examine whether this dysfunction influences the clinical outcome, we explored the distal renal tubular acidification function in patients with PHPT and its effects on the clinical manifestations of the disease.

Methods

We retrospectively analysed 75 PHPT patients with regard to renal tubular acidification and blood gas analysis. The patients were divided into two groups, the renal tubular acidification dysfunction group and normal function group.

Results

Serum phosphate level and total hip bone density were significantly decreased and 25OHD level was significantly increased in the renal tubular acidification dysfunction group in comparison to the normal function group. Female patients in the renal tubular acidification dysfunction group showed significantly decreased femoral neck and total hip BMD and increased susceptibility to fracture. However, there were no such differences in male patients between the two groups.

Conclusions

About 54.6 % of PHPT patients in our study population had abnormal distal renal tubular acidification. PHPT patients with abnormal distal renal tubular acidification may have lower hip bone density. Female PHPT patients with abnormal distal renal tubular acidification showed increased susceptibility to fractures and the development of osteoporosis.

Incomplete distal renal tubular acidosis in children

AIM

To describe incomplete distal renal tubular acidosis (iDRTA) in paediatric patients, a term used for the diagnosis of patients who do not develop spontaneous overt metabolic acidosis but are unable to acidify the urine in response to an ammonium chloride load.

METHODS

Tests used to explore urinary acidification were revised. In addition, publications in English extracted from 161 entries yielded by a PubMed database search, using 'incomplete distal renal tubular acidosis' as keyword, were reviewed.

RESULTS

Incomplete distal renal tubular acidosis has mostly been identified in adults with autoimmune diseases, nephrolithiasis, nephrocalcinosis and/or osteopenia. iDRTA has been reported in few paediatric patients with rickets, congenital abnormalities of kidney and urological tract and/or growth failure. The pathophysiological mechanisms potentially responsible for the defect of urinary acidification are discussed as well as the clinical and biochemical findings of iDRTA described in children.

CONCLUSION

The presentation of iDRTA in children differs from adults. The clinical and biochemical features of iDRTA are not well characterised in paediatric patients. The detection of iDRTA in groups of population such as heterozygous carriers of primary DRTA gene mutations and children with hypocitraturia or hypercalciuria might be of clinical interest to better know the pathophysiology and natural history of iDRTA.

Prevalence and factors associated with osteoporosis and fragility fractures in patients with primary Sjögren syndrome

This study aimed at determining socio-demographic and clinical factors of primary Sjögren syndrome (pSS) associated with osteoporosis (OP) and fragility fracture. SJOGRENSER is a cross-sectional study of patients with pSS, classified according to American European consensus criteria developed in 33 Spanish rheumatology departments. Epidemiological, clinical, serological and treatment data were collected and a descriptive analysis was conducted. Bivariate and multivariate analyses were performed using a binomial logistic regression to study the factors associated with OP and fragility fracture in pSS. 437 patients were included (95% women, with a median age of 58.6 years). 300 women were menopausal (76.4%). Prevalence of OP was 18.5% [in men (N = 21) this measured 19%]. A total of 37 fragility fractures were recorded. In the multivariate analysis, there was an association between OP and age: in the 51-64 age range (menopausal women), the OR measured 9.993 (95% CI 2301-43,399, p = 0.002); In the age > 64 years group, OR was 20.610 (4.679-90.774, p < 0.001); between OP and disease duration, OR was 1.046 (1.008-1085, p = 0.017); past treatment with corticosteroids, OR 2.548 (1.271-5.105, p = 0.008). Similarly, an association was found between fragility fractures and age: in the 51-64 age group, OR measured 5.068 (1.117-22,995, p = 0.035), age > 64 years, OR was 7.674 (1.675-35,151, p < 0.009); disease duration, OR 1.049 (CI 1.003-1097, p < 0.036) and the ESSDAI index, OR 1.080 (1.029-1134, p = 0.002). Patients with pSS can develop osteoporosis and fragility fractures over the course of the disease. Age, corticosteroids treatment and disease duration were associated with the development of OP. Disease duration and ESSDAI were associated with the development of fractures in patients with pSS.

Combination of furosemide and fludrocortisone as a loading test for diagnosis of distal renal tubular acidosis in a pediatric case

Renal tubular acidosis (RTA) is a rare disease caused by a defect of urinary acidification. The ammonium chloride loading test is the gold standard method for determining the type of RTA. However, because this test has some side effects (e.g., nausea, vomiting, and stomach discomfort), applying this test for pediatric cases is difficult. Recently, a loading test with the combination of furosemide and fludrocortisone was reported to be an alternative to the ammonium chloride loading test, with 100% sensitivity and specificity in adult's cases. We report the first pediatric case of distal RTA in a patient who was successfully diagnosed by a drug loading test with the combination of furosemide and fludrocortisone without any side effects. We also performed genetic analysis and detected a known pathogenic variant in the SLC4A1 gene. The combination loading test of furosemide and fludrocortisone is a useful and safe diagnostic tool for pediatric cases of RTA.

Distal renal tubular acidosis: genetic causes and management

BACKGROUND

Distal renal tubular acidosis (dRTA) is a kidney tubulopathy that causes a state of normal anion gap metabolic acidosis due to impairment of urine acidification. This review aims to summarize the etiology, pathophysiology, clinical findings, diagnosis and therapeutic approach of dRTA, with emphasis on genetic causes of dRTA.

DATA SOURCES

Literature reviews and original research articles from databases, including PubMed and Google Scholar. Manual searching was performed to identify additional studies about dRTA.

RESULTS

dRTA is characterized as the dysfunction of the distal urinary acidification, leading to metabolic acidosis. In pediatric patients, the most frequent etiology of dRTA is the genetic alteration of genes responsible for the codification of distal tubule channels, whereas, in adult patients, dRTA is more commonly secondary to autoimmune diseases, use of medications and uropathies. Patients with dRTA exhibit failure to thrive and important laboratory alterations, which are used to define the diagnosis. The oral alkali and potassium supplementation can correct the biochemical defects, improve clinical manifestations and avoid nephrolithiasis and nephrocalcinosis.

CONCLUSIONS

dRTA is a multifactorial disease leading to several clinical manifestations. Clinical and laboratory alterations can be corrected by alkali replacement therapy.

Distal renal tubular acidosis and severe hypokalemia: a case report and review of the literature

Background

Distal renal tubular acidosis is a relatively infrequent condition with complex pathophysiology that can present with life-threatening electrolyte abnormalities.

Case presentation

We describe a case of a 57-year-old Caucasian woman with previous episodes of hypokalemia, severe muscle weakness, and fatigue. Upon further questioning, symptoms of dry eye and dry mouth became evident. Initial evaluation revealed hyperchloremic metabolic acidosis, severe hypokalemia, persistent alkaline urine, and a positive urinary anion gap, suggestive of distal renal tubular acidosis. Additional laboratory workup and renal biopsy led to the diagnosis of primary Sjögren’s syndrome with associated acute tubulointerstitial nephritis. After potassium and bicarbonate supplementation, immunomodulatory therapy with hydroxychloroquine, azathioprine, and prednisone was started. Nonetheless, her renal function failed to improve and remained steady with an estimated glomerular filtration rate of 42 ml/min/1.73 m². The literature on this topic was reviewed.

Conclusions

Cases of renal tubular acidosis should be carefully evaluated to prevent adverse complications, uncover a potentially treatable condition, and prevent the progression to chronic kidney disease. Repeated episodes of unexplained hypokalemia could be an important clue for diagnosis.

Improving outcomes for patients with distal renal tubular acidosis: recent advances and challenges ahead

Primary distal renal tubular acidosis (dRTA) is a rare genetic disorder caused by impaired distal acidification due to a failure of type A intercalated cells (A-ICs) in the collecting tubule. dRTA is characterized by persistent hyperchloremia, a normal plasma anion gap, and the inability to maximally lower urinary pH in the presence of systemic metabolic acidosis. Common clinical features of dRTA include vomiting, failure to thrive, polyuria, hypercalciuria, hypocitraturia, nephrocalcinosis, nephrolithiasis, growth delay, and rickets. Mutations in genes encoding three distinct transport proteins in A-ICs have been identified as causes of dRTA, including the B1/ATP6V1B1 and a4/ATP6V0A4 subunits of the vacuolar-type H⁺-ATPase (H⁺-ATPase) and the chloride–bicarbonate exchanger AE1/SLC4A1. Homozygous or compound heterozygous mutations in ATP6V1B1 and ATP6V0A4 lead to autosomal recessive (AR) dRTA. dRTA caused by SLC4A1 mutations can occur with either autosomal dominant or AR transmission. Red blood cell abnormalities have been associated with AR dRTA due to SLC4A1 mutations, including hereditary spherocytosis, Southeast Asia ovalocytosis, and others. Some patients with dRTA exhibit atypical clinical features, including transient and reversible proximal tubular dysfunction and hyperammonemia. Incomplete dRTA presents with inadequate urinary acidification, but without spontaneous metabolic acidosis and recurrent urinary stones. Heterozygous mutations in the AE1 or H⁺-ATPase genes have recently been reported in patients with incomplete dRTA. Early and sufficient doses of alkali treatment are needed for patients with dRTA. Normalized serum bicarbonate, urinary calcium excretion, urinary low-molecular-weight protein levels, and growth rate are good markers of adherence to and/or efficacy of treatment. The prognosis of dRTA is generally good in patients with appropriate treatment. However, recent studies showed an increased frequency of chronic kidney disease (CKD) in patients with dRTA during long-term follow-up. The precise pathogenic mechanisms of CKD in patients with dRTA are unknown.

Osteoporosis complicating some inborn or acquired diseases

Osteoporosis in chronic diseases is very frequent and pathogenetically varied. It complicates the course of the underlying disease by the occurrence of fractures, which aggravate the quality of life and increase the mortality of patients from the underlying disease. The secondary deterioration of bone quality in chronic diseases, such as diabetes of type 1 and type 2 and/or other endocrine and metabolic disorders, as well as inflammatory diseases, including rheumatoid arthritis - are mostly associated with structural changes to collagen, altered bone turnover, increased cortical porosity and damage to the trabecular and cortical microarchitecture. Mechanisms of development of osteoporosis in some inborn or acquired disorders are discussed.

Incomplete Distal Renal Tubular Acidosis and Kidney Stones

Renal tubular acidosis (RTA) is comprised of a diverse group of congenital or acquired diseases with the common denominator of defective renal acid excretion with protean manifestation, but in adults, recurrent kidney stones and nephrocalcinosis are mainly found in presentation. Calcium phosphate (CaP) stones and nephrocalcinosis are frequently encountered in distal hypokalemic RTA type I. Alkaline urinary pH, hypocitraturia, and, less frequently, hypercalciuria are the tripartite lithogenic factors in distal RTA (dRTA) predisposing to CaP stone formation; the latter 2 are also commonly encountered in other causes of urolithiasis. Although the full blown syndrome is easily diagnosed by conventional clinical criteria, an attenuated forme fruste called incomplete dRTA typically evades clinical testing and is only uncovered by provocative acid-loading challenges. Stone formers (SFs) that cannot acidify urine of pH < 5.3 during acid loading are considered to have incomplete dRTA. However, urinary acidification capacity is not a dichotomous but rather a continuous trait, so incomplete dRTA is not a distinct entity but may be one end of a spectrum. Recent findings suggest that incomplete dRTA can be attributed to heterozygous carriers of hypofunctional V-ATPase. The value of incomplete dRTA diagnosis by provocative testing and genotyping candidate genes is a valuable research tool, but it remains unclear at the moment whether they alter clinical practice and needs further clarification. No randomized controlled trials have been performed in SFs with dRTA or CaP stones, and until such data are available, treatment of CaP stones are centered on reversing the biochemical abnormalities encountered in the metabolic workup. SFs with type I dRTA should receive alkali therapy, preferentially in the form of K-citrate delivered judiciously to treat the chronic acid retention that drives both stone formation and bone disease.

Pseudo-Renal Tubular Acidosis: Conditions Mimicking Renal Tubular Acidosis

Hyperchloremic metabolic acidosis, particularly renal tubular acidosis, can pose diagnostic challenges. The laboratory phenotype of a low total carbon dioxide content, normal anion gap, and hyperchloremia may be misconstrued as hypobicarbonatemia from renal tubular acidosis. Several disorders can mimic renal tubular acidosis, and these must be appropriately diagnosed to prevent inadvertent and inappropriate application of alkali therapy. Key physiologic principles and limitations in the assessment of renal acid handling that can pose diagnostic challenges are enumerated.

Renal Tubular Acidosis: H+/Base and Ammonia Transport Abnormalities and Clinical Syndromes

Renal tubular acidosis (RTA) represents a group of diseases characterized by (1) a normal anion gap metabolic acidosis; (2) abnormalities in renal HCO3- absorption or new renal HCO3- generation; (3) changes in renal NH4+, Ca2+, K+, and H2O homeostasis; and (4) extrarenal manifestations that provide etiologic diagnostic clues. The focus of this review is to give a general overview of the pathogenesis of the various clinical syndromes causing RTA with a particular emphasis on type I (hypokalemic distal RTA) and type II (proximal) RTA while reviewing their pathogenesis from a physiological "bottom-up" approach. In addition, the factors involved in the generation of metabolic acidosis in both type I and II RTA are reviewed highlighting the importance of altered renal ammonia production/partitioning and new HCO3- generation. Our understanding of the underlying tubular transport and extrarenal abnormalities has significantly improved since the first recognition of RTA as a clinical entity because of significant advances in clinical acid-base chemistry, whole tubule and single-cell H+/base transport, and the molecular characterization of the various transporters and channels that are functionally affected in patients with RTA. Despite these advances, additional studies are needed to address the underlying mechanisms involved in hypokalemia, altered ammonia production/partitioning, hypercalciuria, nephrocalcinosis, cystic abnormalities, and CKD progression in these patients.

Renal tubular acidosis

PURPOSE OF REVIEW

To facilitate the understanding and knowledge of renal tubular acidosis by providing a summarized information on the known clinical and biochemical characteristics of this group of diseases, by updating the genetic and molecular bases of the primary forms renal tubular acidosis and by examining some issues regarding the diagnosis of distal renal tubular acidosis (RTA) in the daily clinical practice.

RECENT FINDINGS

The manuscript presents recent findings on the potential of next-generation sequencing to disclose new pathogenic variants in patients with a clinical diagnosis of primary RTA and negative Sanger sequencing of known genes. The current review emphasizes the importance of measuring urinary ammonium for a correct clinical approach to the patients with metabolic acidosis and discusses the diagnosis of incomplete distal RTA.

SUMMARY

We briefly update the current information on RTA, put forward the need of additional studies in children to validate urinary indexes used in the diagnosis of RTA and offer a perspective on diagnostic genetic tests.

Abnormal distal renal tubular acidification in patients with low bone mass: prevalence and impact of alkali treatment

Chronic acid retention is known to promote bone dissolution. In this study, 23 % of patients with osteopenia/osteoporosis were diagnosed with abnormal distal renal tubular acidification (dRTA), a kidney dysfunction leading to chronic acid retention. Treating those patients with alkali-therapy shows improvement in bone density. To evaluate the prevalence of abnormal distal renal tubular acidification in patients with low bone mass (LBM) and the impact of additional alkali treatment on bone density in patients with concomitant LBM and dRTA,183 patients referred for metabolic evaluation of densitometrically proven low bone mass were screened for abnormal distal renal tubular acidification between 2006 and 2013. In all LBM urine pH (U-pH) was measured in the 2nd morning urines after 12 h of fasting. If U-pH was ≥5.80, LBM underwent a 1-day ammonium chloride loading, and U-pH was remeasured the next morning. If U-pH after acid loading did not drop below 5.45, patients were diagnosed with abnormal distal renal tubular acidification. Normal values were obtained from 21 healthy controls. All LBM with dRTA were recommended alkali citrate in addition to conventional therapy of LBM, and follow-up DXAs were obtained until 2014. 85 LBM underwent NH₄Cl loading. 42 LBM patients were diagnosed with incomplete dRTA (idRTA; prevalence 23.0 %). During follow-up (1.6-8 years) of idRTA-LBM patients, subjects adhering to alkali treatment tended to improve BMD at all sites measured, whereas BMD of non-adherent idRTA patients worsened/remained unchanged. (1) About one out of four patients with osteopenia/osteoporosis has idRTA. (2) Upon NH₄Cl loading, idRTA patients do not lower urine pH normally, but show signs of increased acid-buffering by bone dissolution. (3) In idRTA patients with low bone mass on conventional therapy, additional long-term alkali treatment improves bone mass at lumbar spine and potentially at other bone sites. (4) All patients with low bone mass undergoing metabolic evaluation should be screened for idRTA.

Bone Mineral Density in Sjögren Syndrome Patients with and Without Distal Renal Tubular Acidosis

Primary Sjögren's syndrome (pSS) can be complicated by distal renal tubular acidosis (dRTA), which may contribute to low bone mineral density (BMD). Our objective was to evaluate BMD in pSS patients with and without dRTA as compared with healthy controls. BMD of lumbar spine (LS) and femoral neck (FN) was measured in 54 pSS patients and 162 healthy age- and sex-matched controls by dual-energy X-ray absorptiometry (DXA). dRTA was defined as inability to reach urinary pH <5.3 after an ammonium chloride (NH4Cl) test. LS- and FN-BMD were significantly higher in pSS patients compared with controls (1.18 ± 0.21 g/cm(2) for patients vs. 1.10 ± 0.18 g/cm(2) for controls, P = 0.008 and 0.9 ± 0.16 g/cm(2) for patients vs. 0.85 ± 0.13 g/cm(2) for controls, P = 0.009, respectively). After adjustment for BMI and smoking, the LS- and FN-BMD remained significantly higher. Patients with dRTA (N = 15) did not have a significantly different LS- and FN-BMD compared with those without dRTA (N = 39) after adjustment for BMI, age, and gender. Thirty-seven (69 %) pSS patients were using hydroxychloroquine (HCQ). Unexpectedly, pSS patients had a significantly higher LS- and FN-BMD compared with healthy controls. Patients with dRTA had similar BMD compared with patients without dRTA. We postulate that an explanation for the higher BMD in pSS patients may be the frequent use of HCQ.

Clinical and laboratory approaches in the diagnosis of renal tubular acidosis

In the absence of a gastrointestinal origin, a maintained hyperchloremic metabolic acidosis must raise the diagnostic suspicion of renal tubular acidosis (RTA). Unlike adults, in whom RTA is usually secondary to acquired causes, children most often have primary forms of RTA resulting from an inherited genetic defect in the tubular proteins involved in the renal regulation of acid-base homeostasis. According to their pathophysiological basis, four types of RTA are distinguished. Distal type 1 RTA, proximal type 2 RTA, mixed-type 3 RTA, and type 4 RTA can be differentiated based on the family history, the presenting manifestations, the biochemical profile, and the radiological findings. Functional tests to explore the proximal wasting of bicarbonate and the urinary acidification capacity are also useful diagnostic tools. Although currently the molecular basis of the disease can frequently be discovered by gene analysis, patients with RTA must undergo a detailed clinical study and laboratory work-up in order to understand the pathophysiology of the disease and to warrant a correct and accurate diagnosis.

Renal tubular acidosis is highly prevalent in critically ill patients

Introduction

Hyperchloremic acidosis is frequent in critically ill patients. Renal tubular acidosis (RTA) may contribute to acidemia in the state of hyperchloremic acidosis, but the prevalence of RTA has never been studied in critically ill patients. Therefore, we aimed to investigate the prevalence, type, and possible risk factors of RTA in critically ill patients using a physical-chemical approach.

Methods

This prospective, observational trial was conducted in a medical ICU of a university hospital. One hundred consecutive critically ill patients at the age ≥18, expected to stay in the ICU for ≥24 h, with the clinical necessity for a urinary catheter and the absence of anuria were included.

Base excess (BE) subset calculation based on a physical-chemical approach on the first 7 days after ICU admission was used to compare the effects of free water, chloride, albumin, and unmeasured anions on the standard base excess. Calculation of the urine osmolal gap (UOG) - as an approximate measure of the unmeasured urine cation NH₄⁺ - served as determinate between renal and extrarenal bicarbonate loss in the state of hyperchloremic acidosis.

Results

During the first week of ICU stay 43 of the patients presented with hyperchloremic acidosis on one or more days represented as pronounced negative BE_Chloride. In 31 patients hyperchloremic acidosis was associated with RTA characterized by a UOG ≤150 mosmol/kg in combination with preserved renal function. However, in 26 of the 31 patients with RTA metabolic acidosis was neutralized by other acid-base disturbances leading to a normal arterial pH.

Conclusions

RTA is highly prevalent in critically ill patients with hyperchloremic acidosis, whereas it is often neutralized by the simultaneous occurrence of other acid-base disturbances.

Trial registration

Clinicaltrials.gov NCT02392091. Registered 17 March 2015

The long-term complications of the inherited tubulopathies: an adult perspective

The inherited tubulopathies are lifelong disorders and their clinical features and complications may present quite different challenges in adulthood from those in childhood. In this review we outline the pathophysiology and documented complications (including the late and unusual) of the monogenic tubulopathies from the perspective of the adult nephrologist.

Incomplete distal renal tubular acidosis with nephrocalcinosis

We report the case of a female patient with incomplete distal renal tubular acidosis with nephrocalcinosis. She was admitted to the hospital because of acute pyelonephritis. Imaging studies showed dual medullary nephrocalcinosis. Subsequent evaluations revealed hypokalemia, hypocalcemia, hypercalciuria, and hypocitraturia with normal acid-base status. A modified tubular acidification test with NH4Cl confirmed a defect of urine acidification, which is compatible with incomplete distal tubular acidosis. We treated our patient with potassium citrate, which corrects hypokalemia and prevents further deposition of calcium salts.

Distal renal tubular acidosis, hypokalemic paralysis, nephrocalcinosis, primary hypothyroidism, growth retardation, osteomalacia and osteoporosis leading to pathological fracture: a case report

Renal tubular acidosis (RTA) is a constellation of syndromes arising from different derangements of tubular acid transport. Recent advances in the biology of urinary acidification have allowed us to discern various molecular mechanisms responsible for these syndromes. RTA often presents as renal stone disease with nephrocalcinosis, ricket/osteomalacia and growth retardation in children with ultimate short stature in adulthood. The case reported here has features of distal renal tubular acidosis (dRTA), hypokalemic paralysis, primary hypothyroidism, growth retardation, osteomalacia and osteopenia leading to stress fracture. All these features presenting in a single case (as in our case) is a rare occurrence, so far other cases of distal renal tubular acidosis (dRTA) have been reported.

Prevalence and densitometric characteristics of incomplete distal renal tubular acidosis in men with recurrent calcium nephrolithiasis

The aim of this study was to assess the prevalence of incomplete distal renal tubular acidosis (idRTA) in men with recurrent calcium nephrolithiasis and its potential impact on bone mineral density. We conducted a retrospective analysis of 150 consecutive, male idiopathic recurrent calcium stone formers (RCSFs), which had originally been referred to the tertiary care stone center of the University Hospital of Berne for further metabolic evaluation. All RCSFs had been maintained on a free-choice diet while collecting two 24-h urine samples and delivered second morning urine samples after 12 h fasting. Among 12 RCSFs with a fasting urine pH >5.8, a modified 3-day ammonium chloride loading test identified idRTA in 10 patients (urine pH >5.32, idRTA group). We matched to each idRTA subject 5 control subjects from the 150 RCSFs, primary by BMI and then by age, i.e., 50 patients, without any acidification defect (non-RTA group) for comparative biochemistry and dual energy X-ray absorptiometry (DEXA) analyses. The prevalence of primary idRTA among RCSFs was 6.7% (10/150). Patients with idRTA had significantly higher 2-h fasting and 24-h urine pH (2-h urine pH: 6.6 ± 0.4 vs. 5.2 ± 0.1, p = 0.001; 24-h urine pH: 6.1 ± 0.2 vs. 5.3 ± 0.3, p = 0.001), 24-h urinary calcium excretion (7.70 ± 1.75 vs. 5.69 ± 1.73 mmol/d, p = 0.02), but significantly lower 24-h urinary urea excretion (323 ± 53 vs. 399 ± 114 mmol/d, p = 0.01), urinary citrate levels (2.32 ± 0.82 vs. 3.01 ± 0.72 mmol/d, p = 0.04) and renal phosphate threshold normalized for the glomerular filtration rate (TmPO(4)/GFR: 0.66 ± 0.17 vs. 0.82 ± 0.21, p = 0.03) compared to non-RTA patients. No significant difference in bone mineral density (BMD) was found between idRTA and non-RTA patients for the lumbar spine (LS BMD (g/cm(2)): 1.046 ± 0.245 SD vs. 1.005 ± 0.119 SD, p = 0.42) or femoral neck (FN BMD (g/cm(2)): 0.830 ± 0.135 SD vs. 0.852 ± 0.127 SD). Thus, idRTA occurs in 1 in 15 male RCSFs and should be sought in all recurrent calcium nephrolithiasis patients. Bone mineral density, however, does not appear to be significantly affected by idRTA.

Amelioration of hypophosphatemic rickets and osteoporosis with pamidronate and growth hormone in Lowe syndrome

The oculocerebrorenal syndrome of Lowe, an X-linked multisystem disorder, was diagnosed in a male patient who presented with typical abnormalities of the eyes, kidneys and nervous system. Besides congenital cataracts, renal tubular dysfunction and psychomotor retardation, the patient had also suffered from profound failure to thrive, growth hormone deficiency, severe osteoporosis with hypophosphatemic rickets, and progressive renal dysfunction since early childhood, which were attributed to the metabolic derangements following Fanconi syndrome. Direct sequencing of the OCRL1 gene (responsible for the oculocerebrorenal syndrome of Lowe) revealed a de novo c.2282_2283insT in exon 20, which resulted in premature termination of translation (D762X). After monthly intravenous administration of pamidronate since the age of 17.8 years, his urine creatinine clearance and tubular resorption of phosphate increased slightly and bone mineral density was much improved (Z score increased from -7.3 to -3.3) without deterioration of renal function. Simultaneous growth hormone therapy enhanced the positive response. The beneficial osseous and renal effects of the bisphosphonate, along with growth hormone treatment in Lowe syndrome with hypophosphatemia, may be related to reduced renal calcium and phosphate excretion.

Bicarbonate therapy improves growth in children with incomplete distal renal tubular acidosis

Incomplete distal renal tubular acidosis (idRTA) has recently been associated with osteoporosis and growth retardation, attributed to the mild persistent metabolic acidosis. We hypothesized a therapeutic benefit from bicarbonate therapy on growth parameters in children with idRTA. In a study group of 40 surgically treated patients with posterior urethral valve (PUV) and normal estimated glomerular filtration rate, we evaluated the change in height standard deviation scores (SDSs) while they were on bicarbonate therapy in the presence of idRTA and complete distal renal tubular acidosis (dRTA). Age- and gender-matched healthy subjects constituted the control group (n = 55). Incomplete dRTA was evaluated by ammonium chloride acidification. The baseline height SDS of -1.94 +/- 0.41 and -5.31 +/- 1.95 in the groups with idRTA and complete dRTA, respectively, were significantly lower than that of the controls. After a follow-up period of 24.7 +/- 8.3 months on sodium bicarbonate therapy, the idRTA patients had a 66% increase in height SDS compared with 26% and 3% increases in the patients with PUV with complete dRTA and without dRTA, respectively. At the end of follow-up, mean height SDS in the group with idRTA no longer remained significantly lower than that of the controls (P = 0.42). We concluded that bicarbonate therapy improves height SDS in idRTA. This issue needs further validation in larger studies.

Low bone density in children with hypercalciuria and/or nephrolithiasis

The objective of this study was to identify how many children with hypercalciuria and/or nephrolithiasis have a low bone density and whether the risk of low bone density can be identified by 24-h urine stone-risk profiles and/or growth parameters. A retrospective chart review was performed on 110 idiopathic hypercalciuria and/or kidney stone patients who received both a 24-h urine for stone-risk profile and a dual-energy X-ray densitometry scan. Patients were divided into low bone density vs. normal bone density groups and hypercalcuria verus nephrolithiasis groups and analyzed for differences in growth parameters, urine stone-risk profiles, and bone densities. Overall, 47% had a bone density z score < -1, and 26% had a bone density z score < -2. Patients with a low bone density had a higher body mass index and lower urine creatinine and ammonium than those with a normal bone density. Patients with nephrolithiasis had a lower bone density z score than patients with hypercalcuria and no nephrolithiasis. Clinicians should be aware of the increased incidence of low bone density in children with hypercalciuria and nephrolithiasis. The effect of hypercalciuria and nephrolithiasis treatment on bone density and the natural progression of the bone density in the studied patient population warrants further investigation.

Distal renal tubular acidosis and ovalocytosis: a case report

A 23-year-old man presented with osteoporosis, revealed by femoral fractures, and a history of nephrolithiasis, short stature, metabolic acidosis, hypokalemia and ovalocytosis, a red blood cell abnormality common in malaria endemic regions. Biological investigations led to the diagnosis of type 1 distal renal tubular acidosis (dRTA). Ovalocytosis and dRTA may co-exist in the same patient, since both can originate in mutations of the anion-exchanger 1 (AE1) gene, which codes for band 3, the bicarbonate/chloride exchanger, present in both the red cell membrane and the basolateral membrane of the collecting tubule alpha-intercalated cell.

Inadequate dietary intake but not renal tubular acidosis is associated with bone demineralization in primary biliary cirrhosis

BACKGROUND

Metabolic bone disease associated with primary biliary cirrhosis (PBC) is inadequately characterized. Renal tubular acidosis (RTA) may lead to bone loss through chronic mobilization of skeletal calcium salts to buffer increased acid load.

AIM

To evaluate the prevalence of RTA in PBC and establish the relationships among bone mineral density (BMD), renal function and nutritional status.

METHODS

We enrolled 69 female patients with compensated PBC and 35 control patients with chronic hepatitis C. RTA was searched in all patients, and 24-h dietary recalls were collected at enrolment. BMD was measured by dual-energy X-ray absorptiometry at the femur neck, lumbar spine and radius ultradistalis sites.

RESULTS

No patients received a diagnosis of RTA. BMD values (Z-scores) showed only little deviation from normal population with no difference between PBC and controls. Osteopoenic PBC patients (T-score < 1) showed significantly lower daily phosphorus intake [median: 672 (288-1374) vs. 921 (253-1923) mg/day; P = 0.037], with a trend towards lower caloric intake than their nonosteopoenic counterparts.

CONCLUSIONS

Renal tubular acidosis is uncommon in compensated PBC. Cholestasis is not associated with an increased risk of bone demineralization. Inadequate dietary intake may be a preventable factor contributing to bone loss in PBC.

Renal tubular acidosis: developments in our understanding of the molecular basis

Renal tubular acidosis is a metabolic acidosis due to impaired acid excretion by the kidney. Hyperchloraemic acidosis with a normal anion gap and normal (or near normal) glomerular filtration rate, and in the absence of diarrhoea, defines this disorder. However, systemic acidosis is not always evident and renal tubular acidosis can present with hypokalaemia, medullary nephrocalcinosis and recurrent calcium phosphate stone disease, as well as growth retardation and rickets in children, or short stature and osteomalacia in adults. Renal dysfunction in renal tubular acidosis is not always confined to acid excretion and can be part of a more generalised renal tubule defect, as in the renal Fanconi syndrome. Isolated renal tubular acidosis is more usually acquired, due to drugs, autoimmune disease, post-obstructive uropathy or any cause of medullary nephrocalcinosis. Less commonly, it is inherited and may be associated with deafness, osteopetrosis or ocular abnormalities. The clinical classification of renal tubular acidosis has been correlated with our current physiological model of how the nephron excretes acid, and this has facilitated genetic studies that have identified mutations in several genes encoding acid and base ion transporters. In vitro functional studies of these mutant proteins in cell expression systems have helped to elucidate the molecular mechanisms underlying renal tubular acidosis, which ultimately may lead to new therapeutic options in what is still treatment only by giving an oral alkali.

[Primary and secondary osteoporosis. The important role of internal medicine in its differential diagnosis]

Bone metabolism as an important part of internal medicine is covered by endocrinologists, rheumatologists and nephrologists. Primary osteoporosis is an inheritable metabolic bone disease, which can be strongly modified by lifestyle, ageing and underlying diseases. Chronic inflammatory diseases, disorders of metabolism and nutritional deficits enhance the risk. Secondary osteoporosis is caused by endocrinological disorders and drugs such as glucocorticoids. It is the task of internists to clinically recognise and diagnose prominent individual risk factors for primary osteoporosis and underlying diseases for secondary osteoporosis. The key competence of internal medicine in metabolism, hormone-related disorders, malignant diseases and in handling complex medical treatment modalities represents an indispensable segment of an interdisciplinary network approach in patient care, research and teaching. This network includes orthopaedic surgery, paediatrics and gynaecology in addition to other specialties.

Genetic ablation of Rhbg in the mouse does not impair renal ammonium excretion

NH(4)(+) transport by the distal nephron and NH(4)(+) detoxification by the liver are critical for achieving regulation of acid-base balance and to avoid hyperammonemic hepatic encephalopathy, respectively. Therefore, it has been proposed that rhesus type B glycoprotein (Rhbg), a member of the Mep/Amt/Rh NH(3) channel superfamily, may be involved in some forms of distal tubular acidosis and congenital hyperammonemia. We have tested this hypothesis by inactivating the RHbg gene in the mouse by insertional mutagenesis. Histochemical studies analyses confirmed that RHbg knockout (KO) mice did not express Rhbg protein. Under basal conditions, the KO mice did not exhibit encephalopathy and survived well. They did not exhibit hallmarks of distal tubular acidosis because neither acid-base status, serum potassium concentration, nor bone mineral density was altered by RHbg disruption. They did not have hyperammonemia or disturbed hepatic NH(3) metabolism. Moreover, the KO mice adapted to a chronic acid-loading challenge by increasing urinary NH(4)(+) excretion as well as their wild-type controls. Finally, transepithelial NH(3) diffusive permeability, or NH(3) and NH(4)(+) entry across the basolateral membrane of cortical collecting duct cells, measured by in vitro microperfusion of collecting duct from KO and wild-type mice, was identical with no apparent effect of the absence of Rhbg protein. We conclude that Rhbg is not a critical determinant of NH(4)(+) excretion by the kidney and of NH(4)(+) detoxification by the liver in vivo.

Bone disease in primary biliary cirrhosis: lack of association with distal renal tubular acidosis

BACKGROUND AND AIMS

Primary biliary cirrhosis (PBC) might be complicated by osteoporosis, whose etiology remains unknown but seems to be multifactorial. Prevalence rates of 30% to 60% for distal renal tubular acidosis (DRTA) have been reported in PBC patients, generally as incomplete DRTA. Although it is undisputed that a reduced bone mineral density (BMD) is the expected outcome among patients who have been suffering from longstanding chronic metabolic acidosis, it is unclear if incomplete DRTA is also associated with metabolic bone disease in PBC patients. The present study was undertaken to compare the BMD of PBC patients with and without DRTA.

METHODS

The BMD of 23 PBC patients (11 with DRTA and 12 without), all with normal clearance of creatinine, was assessed by dual energy radiograph absorptiometry. The diagnosis of DRTA was made if the urine pH was above 5.4 in all samples after the oral acid overload, showing tubular inability to acidify urine in the presence of test-induced systemic metabolic acidosis.

RESULTS

Densitometric signs of osteoporosis were found in 82% of DRTA cases and in 83% of patients without DRTA (difference not significant). There were no significant differences in BMD measurement, T and Z scores of patients with and without DRTA.

CONCLUSIONS

The present study could not support a correlation between the presence of DRTA and the bone loss observed in PBC patients.

Incomplete renal tubular acidosis and bone mineral density: a population survey in an area of endemic renal tubular acidosis

BACKGROUND

'Primary' osteoporosis has been associated with a high incidence of a renal acidification defect, incomplete renal tubular acidosis (iRTA). An acid loading test, to exclude the defect, has been recommended for inclusion in the work-up of osteoporosis. However, there is no community-based study to confirm its utility.

METHOD

A community-based survey was conducted in the Khon Kaen province, Thailand, between January and June, 2000. We randomly enrolled 361 apparently healthy adults, 146 men and 215 women, in this study. The bone mineral densities (BMDs) of the spine and femur were determined in all subjects. The diagnosis of iRTA was based on: normal serum electrolytes and one or both of first morning urinary pH >5.5 or the failure of an acid loading test to decrease it to >5.5. Dietary diaries, serum electrolyte tests and 24 h urine collections were obtained from all iRTA subjects.

RESULTS

There were 23 (6.4%) iRTA subjects in the population studied. The age, height, weight and calcium intake were comparable between iRTA and normal subjects, as were the BMDs of spine and femur. There was no difference between the two groups in the distributions of BMD with age for either area. Multiple regression analyses of the studied population demonstrated that age, body weight, duration of menopause and gender (only for the femoral neck) were independent variables that affected BMD.

CONCLUSION

Incomplete distal renal tubular acidosis alone was not associated with lower bone mass in this cohort. It may nevertheless be valuable to monitor serum electrolytes and BMD in patients with iRTA due to their tendency to develop intermittent metabolic acidosis.

Alteration of noncollagenous bone matrix proteins in distal renal tubular acidosis

Our previous report on bone histomorphometry in patients with distal renal tubular acidosis (dRTA) revealed decreased bone formation rate (BFR) when compared to healthy subjects. The abnormality improved significantly after alkaline therapy. The modest increase in osteoblastic surface, after correction of metabolic acidosis, could not explain the striking improvement in bone formation, suggesting additional influence of metabolic acidosis on osteoblast function and/or bone matrix mineralization. Osteoblasts and, to a lesser extent, osteoclasts synthesize and secrete bone matrix including type I collagen and various noncollagenous proteins (NCPs). Substantial evidence suggested diverse functions of NCPs related to bone formation, resorption, and mineralization. Metabolic acidosis, through its effect on bone cells, may result in an alteration in the production of NCPs. Our study examined bone histomorphometry with detailed analysis on the mineralization parameters and NCPs expression within the bone matrix of patients with dRTA before and after treatment with alkaline. Seven dRTA patients underwent bone biopsy at their initial diagnosis and again 12 months after alkaline therapy. Bone mineral density (BMD) and bone histomorphometry were obtained at baseline and after the treatment. The expression of NCPs was examined by immunohistochemistry, quantitated by digital image analysis, and reported as a percentage of area of positive staining or mineralized trabecular bone area. Alkaline therapy normalized the low serum phosphate and PTH during acidosis. The reduction in BMD at baseline improved significantly by the treatment. Bone histomorphometry demonstrated the increase in osteoid surface and volume without significant alteration after acidosis correction. In comparison to the normal subjects, osteoid thickness was slightly but insignificantly elevated. Osteoblast and osteoclast populations and their activities were suppressed. The reduction in mineral apposition rate and adjusted apposition rate were observed in conjunction with the prolongation of mineralization lag time. Alkaline therapy improved the mineralization parameters considerably. In addition to the increase in BFR relative osteoblast number after acidosis correction, osteocalcin expression in the bone matrix increased significantly from 16.7% to 22.3%. Six of seven patients had decreased osteopontin expression. In conclusion, the abnormal bone remodeling in dRTA is characterized by low turnover bone disease with some degree of defective mineralization. Alteration of NCPs expression suggested the effect of metabolic acidosis on bone cells. Alkaline therapy increased bone mass through the restoration of bone mineral balance and, perhaps, improved osteoblast function.

Osteal Complications as First Manifestation in a Patient with Primary Sjogren's Syndrome and with Associated Distal Tubular Acidosis (Type 1) and Chronic Renal Insufficiency

Renal affection is among the complications associated with the Sjögren's Syndrome. Tubulo-interstitial nephritis constitutes the most frequent renal lesion and distal tubular acidosis (Type 1) is the most important clinical manifestation of this tubular dysfunction, although the occurrence of chronic renal insufficiency is not an uncommon finding in the presence of distal renal tubular acidosis. Osteomalacia is a clinical consequence of tubular acidosis caused by buffering of H+ in the bone. We present the case of a woman with osteal complication a year before being diagnosed with primary Sjögren's Syndrome and with distal tubular acidosis and renal insufficiency associated at diagnosis.

Search for occult secondary osteoporosis: impact of identified possible risk factors on bone mineral density

OBJECTIVES

To determine whether the use of more elaborate diagnostic tests can identify possible risk factors for secondary osteoporosis and to evaluate the impact of these possible risk factors on the severity of bone disease in the study population.

DESIGN

Cross-sectional study.

SETTING AND PARTICIPANTS

We have investigated 377 subjects (285 females, 92 males) with osteoporosis (T-score less than -2.5 in dual energy X-ray absorption) or nontraumatic lumbar vertebral fractures; these patients were referred to our hospital, a secondary care centre, for evaluation and treatment of osteoporosis.

RESULTS

Osteoporosis without attributable risk factor was diagnosed in 106 women (37%) and 30 men (33%). In 241 patients (179 women, 62 men) one or more possible risk factors for osteoporosis (in this paper also called subclinical disease) were revealed. The most common were lactose malabsorption, disturbed exocrine pancreatic function and renal tubular disturbances, including renal hypercalciuria, incomplete renal tubular acidosis and mild phosphate diabetes. The number of possible risk factors in the individual patient was significantly related to the severity of osteoporosis as assessed by Z-scores (Spearman correlation r = -0.43, P < 0.001, n = 172 for females; r = -0.28, P < 0.05, n = 65 for males).

CONCLUSIONS

All the identified subclinical diseases would have remained undetected if the currently accepted guidelines for the investigation of patients with osteoporosis were applied. The statistically significant correlation between the number of identified possible risk factors and the severity of bone disease in the individual patient strongly suggests the pathogenetic significance of the identified subclinical diseases. It is yet to be shown, whether specific treatment of these subclinical diseases yields additional improvement of bone mass as compared with standard treatment of osteoporosis.